In thermal inkjet printing systems, a thermal inkjet (TIJ) printhead typically ejects printing fluid drops from a reservoir through a plurality of nozzles onto a print medium. The nozzles are typically arranged in one or more arrays or columns such that properly sequenced ejection of printing fluid from the nozzles causes intended images to be printed on a print medium as the printhead and/or print medium move relative to each other. TIJ printheads eject printing fluid drops from a nozzle by passing electrical current through a heating element, which generates heat and vaporizes a small portion of the printing fluid within a firing chamber. The rapidly expanding vapor bubble forces a small amount of printing fluid to drop out of the nozzle. When the heating element cools, the vapor bubble quickly collapses, drawing more printing fluid from the reservoir into the firing chamber.
During printing, heat from the heating elements as well as the physical configuration and thermal characteristics of the TIJ die affect the temperature of the TIJ die. For instance, the areas, e.g., ends, of the TIJ die that do not contain heating elements often act as heat sinks and thus pull heat from locations in the TIJ die containing heating elements. Thermal differences over the nozzle column area of the TIJ die have a significant influence on characteristics of the printing fluid drops being fired from the nozzles. For example, a higher die temperature results in a higher drop weight and drop velocity, while a lower die temperature results in a lower drop weight and velocity. Thus, variations in temperature across the die have been known to result in variations in drop weight, velocity and shape, which have been known to have a considerable impact on print quality. For example, drops with lower drop weight ejected from cooler areas of the die have been known to result in printed areas on the print medium that have less printing fluid than intended. The areas printed with less printing fluid will appear to be lighter than other areas printed with drops of higher drop weight ejected from warmer areas of the die. In general, print quality problems associated with inconsistent drop characteristics caused by variations in temperature across the TIJ die are referred to as light area banding (LAB), die boundary banding (DBB), and hue shift.